The 21-year-old, who came through the youth system at Sporting, has scored twice in nine appearances for his Portuguese club this season, adding to the seven goals that he managed last term.

The Portugal international also impressed against Real Madrid in the Champions League last month and it is understood that the Spanish giants have been monitoring his progress this season.

According to various reports in Spain, while Real Madrid take on Legia Warsaw in the Champions League on Tuesday, the Spanish giants will have a scouting team in Lisbon to watch the Sporting attacker once again.

Earlier this month, Barcelona's international director of sports Ariedo Braida revealed that the Spanish champions were "observing" Gelson's form ahead of a potential January move.